In the observation and treatment of a biological lumen or the like using an endoscope, a guide wire is employed to introduce the endoscope or a catheter inserted in a lumen of the endoscope to a specific position in the biological lumen or the like.
During insertion of a guide wire, if the guide wire is monochromatic, it is difficult to confirm the axial movement of the guide wire. It is thus preferable to provide a mark on the surface of the guide wire indicating the position or the like. In this regard, various methods have been proposed for providing marks on guide wires.
For example, one known method generally discussed in U.S. Pat. No. 5,379,779 involves preparing a hollow tube made from polytetrafluoroethylene (sold under the trademark Teflon®) with a plurality of colored stripe patterns, inserting a core member of a guide wire in the hollow tube, and bonding the hollow tube to the core member by heat shrink.
However, this method using a hollow tube has disadvantages in that because the mark (colored stripe patterns) is provided simultaneously with the formation of the guide wire, it is difficult to provide the mark at a desired position. Also, there are limitations with respect to the degree of freedom in the shape and width of the mark.
A method of forming a mark on a guide wire by printing is also known and generally discussed in Japanese Utility Model Laid-open No. Hei 4-108556. A method which utilizes printing, however, has disadvantages in that because the ink has little or no resistance against solvent, it is difficult to coat the surface of a guide wire with a lubricating layer made from a hydrophilic polymer or the like after formation of the mark on the surface of the guide wire. In addition, it is difficult to form the mark on a curved surface of the guide wire, and the ink takes a relatively long time to dry and is liable to flow in a living body during use of the guide wire.
A method for addressing these shortcomings is generally discussed in Japanese Utility Model Laid-open No. Hei 4-63054 and involves providing a coating layer made from a transparent fluorocarbon resin on the surface of a guide wire after a mark is provided on the surface of the guide wire by printing.
This improved method, however, has its own disadvantages because it requires additional steps of drying ink and forming the coating layer, thereby complicating the production process. In addition, there is a limitation in design in that only a transparent resin is used for forming the coating layer.
U.S. Pat. No. 4,951,686 discusses a method of heating a color mark formation portion of a catheter introducing wire (guide wire) made from steel at a temperature at which a temper color appears. This method of forming a temper color mark on the surface of the guide wire by heating is disadvantageous in that it can be applied only to a catheter introducing wire made from a steel material. For example, the physical properties of a superelastic alloy (Ni—Ti alloy) generally used as the material of a core member of a guide wire are liable to be changed by heat-treatment such as heating and so this method is not well suited to being applied to a guide wire having a core member made from such a superelastic alloy. U.S. Pat. No. 4,951,686 also describes a method of forming a mark by stamping or irradiation with laser light. However, the formation of a mark by stamping is not well suited to providing a raised marked portion while the formation of a mark by irradiation with laser light is not well suited to providing a recessed marked portion.
At the time of insertion of a guide wire or a catheter to a specific position in a biological lumen or the like via an endoscope, it is oftentimes necessary to overpass the range observable by the endoscope and further advance in a peripheral lumen. In this case, to diagnose such a peripheral lumen, an X-ray contrast agent is injected into the lumen, with the diameter and the shape of the lumen being observed by irradiating the lumen with X-rays. A guide wire to be inserted in a lumen contains an X-ray contrast agent, particularly at the distal end, in order to confirm the position of the distal end.
A guide wire to be inserted via an endoscope, which has a mark visible by an endoscope and also containing an X-ray contrast agent, is known from U.S. Pat. No. 5,379,779 and Japanese Patent Laid-Open No. 2001-46508. According to the method described in Japanese Patent Laid-Open No. 2001-46508, a mark is formed by inserting a core member in a tube having a previously formed pattern, and bonding the tube to the core member by heat shrink, or by coating the core member with a paint. This method thus has similar problems to those mentioned above in connection with the methods discussed in U.S. Pat. No. 5,379,779 and Japanese Utility Model Laid-open No. Hei 4-108556.
A need thus exists for a guide wire having a less lossy marker (a relatively indelible marker less susceptible to peeling, less loss due to dissolution and less fading) possessing the desired size and shape at a desired position while ensuring a relatively high contrastability under X-ray fluoroscopic guidance or the like, with the sharpness of the marker being relatively ensured by suppressing heat generation at the time of formation of the marker.